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SEPG 2149 Date Awarded 2003

Begging and provisioning of Thin-billed prions Pachyptila belcheri is related to testosterone and corticosterone

Petra Quillfeldt, Juan F. Masello, Ian J. Strange & Katherine L. Buchanan

Abstract

1. Vigorous begging is usually seen as an expression of parent-offspring conflict over limited resources. Chicks signal their need by begging, but the evolution of honest msignals requires the signals to be costly. Although some possible costs have been identified, the cost-inducing mechanisms underlying this widely distributed signalling system remain unclear. Because hormones associated with stress and hunger (corticosterone) and aggressive behaviour (testosterone) have deleterious side-effects, the costs of the signal may be coupled to the expression of such hormones, if they are closely associated with the signal.

2. We tested whether begging in chicks of Thin-billed prions Pachyptila belcheri (Procellariiformes, Aves) is associated with secretion of corticosterone and testosterone by the chicks.

3. Prion chicks honestly signalled their nutritional state to their parents. Begging increased with decreased body condition, both within and between chicks. Adults responded to more intense begging by delivering increased meal sizes.

4. We found evidence that corticosterone and testosterone secretion play a major role in this signalling system. The mean body condition of chicks correlated positively with testosterone levels and negatively with corticosterone levels and in a cross-fostering experiment, the change in testosterone and corticosterone between the control period and the experimental period was positively correlated with the change in begging intensity.

5. This is the first direct experimental test suggesting that the control of chick begging by endogenously produced testosterone and corticosterone forms a mechanism controlling parental provisioning in birds and that chick behaviour can explain part of the variation in growth patterns observed between individual birds.

Keywords: endocrine control of signalling, Falkland Islands, honest signalling, parentoffspring conflict, Procellariiformes

Full Report: SEPG2149

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